What is the purpose of the deltaxml:exchange element in the delta file?
NOTE: The deltaxml:exchange element is used in the delta file for versions up to DeltaXML Core 4.5.2. It does not appear at all in versions from DeltaXML 5.0. A deltaxml:exchange element occurs when two data elements at the same position in the input documents are exchanged, i.e. one is deleted and the other added. This means that where there was one item in each of the input documents, there will be one item in the delta file. The rationale behind it is to preserve, as far as possible, the same structure in the delta as in the input documents. For a deltaxml:exchange to occur in the delta file the two items in the input files must be different types, i.e. different element types, elements of the same type but with different keys, or one an element and the other a PCDATA item. The reason that two elements of the same type but with different keys are considered to be different is because DeltaXML will never report that a key has been changed, because it never considers that two elements
